<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>04_JS流程控制</title>
</head>
<body>
<script>
  //1.顺序结构
  console.log('1');
  console.log('2');
  console.log('3');
  //2.分支结构
  let uname=' ';
  if (!uname){
    alert( '请先登录')
  }else {
    alert('欢迎'+uname)
  }
  //3.选择分支
  let gender=10;
  switch (gender){
    case 1:
      console.log('男');
      break;
    case 2:
      console.log('女');
      break;
    default:
      console.log('未知');
  }

  //4.循环结构
  let names=['张三','李四','王五'];
  for (let i = 0; i < names.length; i++){
     console.log(names[i]);
  }
  //如果用var定义循环变量i，循环结束后在此处仍能打印出i的值
  //但如果用let定义，就报错，变量i不存在
  console.log(i);

  //5.增强for循环
  //n为每轮循环遍历到的值 name为被遍历的数组
  for ( let n of names){
    console.log(n);
  }
</script>
</body>
</html>